This invention relates generally to the electrical design and mechanical packaging of electronic components, and more particularly to a method of power conversion utilizing a multiple transformers primaries in series and secondary in parallel.
One approach to packaging electric components in power converters (FIG. 1) includes a housing which both encloses the components and means of heat extraction from the components. The house includes a non-conductive casing 5 and an aluminum heat-sinking base. A printed circuit board (PCB) 3 is mounted next to the upper wall 5a of the casing. Conductive pins 7 are attached directly to the PCB 3 and extend up through the wall 5a. Electronic components 9a, 9c are mounted to one or both sides of the PCB 3. Larger side components such as the transformer 9c are monted to the lower side for space reason. Power dissipating devices such as 9b are mounted directly on the base-plate 6 for better heat transfer. The power components 9b are electrically connected to the PBC by leads 12. Some of the power dissipating devices, 9d, are attached to the base plate via a thermally conductive insulator material 8. Structure 1 may be filled with an encapsulant, which acts as a heat spreader and provides mechanical support. In the case when a hard epoxy encapsulant is used a "buffer coating" material is used to protect some of the components.
In the multiple transformer configuration of this invention, the use of multiple transformers is not new. These multiple secondaries (parallel or not) provide for equal currents but these currents get constricted in the rectifiers and output chokes. Using this type of structure requires large, expensive output chokes and special high current rectifiers which take up precious PCB space. Another drawback to the standard topology is that as device characteristics change over time in the rectifiers and transformers, the currents in the secondaries become more unbalanced while adversely affecting the flux densities in the transformers.
It is clear that there is a need for an improved circuit for multiple transformer systems.